fingerprints - baltimore county public schools
TRANSCRIPT
What Are Fingerprints? Raised ridges of skin
on the hairless surfaces of hands and feet (Dermal Ridges)
Primates and other animals have them
Provide traction and every ridge contains a gland
When Do Fingerprints Form?
Begin to develop in the 10th week of gestation and are complete by the 24th week
Chance, environment, and heredity all play a role in the development of an individuals fingerprints
Three Principals of Fingerprints
1. A fingerprint is an individual characteristic a. No two fingers have the same fingerprint b. Identical twins are similar but not identical
2. Fingerprints remain unchanged during a lifetime
3. Fingerprints have general ridge patterns that permit them to be classified
Three Types of Fingerprints
Plastic Impressions. Made in soft material like butter, soap, etc.
Visible Prints. Prints made when fingers have been covered
in blood, dirt, oil, paint, etc. Latent Prints.
Prints not visible to the human eye, hidden, unseen until treated.
Methods for Making Latent Prints Visible.
Chemical Methods – Iodine fuming – Ninhydrin – Silver Nitrate – Super Glue Fuming
Powder Methods – Black Powder for light surfaces – White powder for dark surfaces
Loops 60% of the worlds
population has them Ridges start on one
side, rise towards the center, and return back to the side they started from
Has 1 delta 2 types of loops
• Radial (thumb) • Ulnar (pinkie)
Arches
5% of the world’s population has them
Start on one side, rise towards the center, then leave on the other side
No deltas 2 Types of arches
• Plain • Tented
Whorls
35% of the worlds population has them
Has some ridges that form circles or spirals Has 2 Deltas
4 types of whorls • Plain • Central Pocket whorl • Double Loop • Accidental whorl
Identification of Minutiae You must find 12
points of minutiae to match a print from a scene of a crime to a person’s print
Label each with a number and a line to show its location
Make a key at the bottom of the two prints
Identification of Minutiae
1. Bifurcation 4. Ridge Ending 7. Bifurcation 2. Bifurcation 5. Enclosure 8. Bifurcation 3. Bifurcation 6. Bifurcation 9. Ridge Ending
Classification of Fingerprints
Two International Systems Henry System – Used in North America and
Europe Vucetich System – Used in Central and South
America Identification is based on class and ridge
patterns (minutiae) found on each individual print
Henry Classification System
Five different levels of classification Primary Classification
Creates a fraction 25% of the world’s population is 1/1
RI + RR + LT + LM + LL + 1 RT RM RL LI LR 1 Whorl = 16,8,4,2,1 Arch and Loop = 0
Primary Classification Example A person has the following combination of
prints on their ten fingers: RT=Arch RI=Whorl RM=Arch RR= Loop RL=Whorl LT=Loop LI=Arch LM=Whorl LR=Whorl LL=Arch
RI/RT + RR/RM + LT/RL + LM/LI + LL/LR + 1/1
16/0 + 0/0 + 0/4 + 2/0 + 0/1 + 1/1 = 19/6
The Primary Classification is 19/6